Over the years various kinds of machines have been developed for cleaning and maintaining floors inside buildings, and paved outdoor areas such as streets, sidewalks and parking lots. They include such machines as rotary broom sweepers, vacuum sweepers, scarifiers, burnishers, polishers and scrubbers. For our purposes here they can be divided into machines which apply water to the surface being maintained and machines which operate dry. We are concerned with the latter, which would include many vacuum sweepers, scarifiers, and rotary broom sweepers. They all share one problem which is addressed by this invention. In their normal operation they tend to stir up dust from the surface being maintained. If it is not controlled, this dust will settle on everything and everybody in the vicinity of the machine, and that is highly objectionable.
On many of these machines the problem has received one general solution. The functional tool which generates the dust, such as a rotary broom, a scarifier head, or a vacuum pickup, is provided with a cover and surrounded by walls which have rubber skirts that hang down almost to the surface being maintained. An on board exhaust blower continuously pulls air from the tool chamber thus created so there is a sub-atmospheric air pressure within it which eliminates outflow of dusty air from under the skirts. The blower exhausts this air to atmosphere. One or more air filters are placed in this air path, either upstream or downstream from the blower, to remove dust from the air before it is released so the discharge to atmosphere will be dust free.
The dust thus removed from the air stream builds up on the filters and in time will block off the airflow through them unless they are periodically cleaned, so a cleaning means is commonly provided which the machine operator must use when needed. Generally the operator must be watchful for dust coming out from under the skirts, which indicates that airflow has been reduced by dust plugging the filters. He or she then must stop the machine, shut off the air flow, and activate the cleaning means. This is most commonly a mechanism that shakes or jolts the filters for a predetermined time to shake off the dust, which falls to a collection tray for later removal. Then the air flow is re-started and the machine operation is resumed. This method is effective when properly carried out, but it takes time away from productive operation. Some operators carelessly neglect doing it when needed, so that dust escapes from the machine while it is operating and settles on objects in the area. Also, filters that are allowed to get too dirty cannot be as effectively cleaned and must be replaced more often than properly serviced filters.
To eliminate these shortcomings it would be desirable to provide an automatic filter cleaning system that would require no attention from the operator and that would function without interrupting the machine operation. There have been efforts in that direction. U.S. Pat. Nos. 4,637,825 and 4,756,727 each show a sweeper filter that is automatically cleaned while the sweeper is operating by directing pulses of compressed air sequentially against segments of the filter from its clean side to blow off dust.
It is common in industry to clean air filters by thus back blasting them with pulses of compressed air. Many industrial machines generate dust, for example, cement mills. Exhaust fans are used to suck the dust into bag houses which contain multiple filters to clean the exhaust air before releasing it to atmosphere. The bag house filters are commonly cleaned by sequentially back blasting them with pulses of compressed air that is obtained from an air compressor on the grounds.
A typical industrial plant needs compressed air for many uses, so the cost of the compressor does not have to be charged entirely to the bag house. Using a back blast system on a surface maintenance machine such as, for example, a sweeper or scarifier, however, requires adding an on board air compressor, an air tank and related valving not otherwise needed. This adds substantial first cost and some maintenance cost to the machine and increases the fuel consumption of its engine, which must pick up the added load of driving the compressor. Also, care must be taken that the pulses of compressed air do not create puffs of dust out from under the skirts.
There are also industrial bag houses in which the bags are cleaned by mechanically shaking them. In these the air flow through them is shut off while the bags are being cleaned. If continuous operation is necessary the bags are installed in a series of compartments so that air can be shut off from one compartment at a time and those bags shaken while the remaining compartments continue to pass air. All the compartments will be cleaned sequentially, one at a time. This cleaning cycle may be set up to operate automatically, triggered by a pressure build-up across the filters. However, this technology has never been applied to mobile surface maintenance machines such as sweepers, vacuum cleaners, scarifiers and the like. The inventors of the present invention were the first to recognize the possibility of doing this and develop a practical way of doing it on mobile equipment of this type.